Rubber composition comprising a specific crumb rubber

ABSTRACT

A rubber composition is based on at least an elastomer, a reinforcing filler and a crosslinking system and a crumb rubber, said crumb having a particle size distribution such that it comprises less than 35% by weight of particles having a size of less than 50 μm and less than 30% by weight of particles having a size of greater than 200 μm.

The invention relates to compositions, especially for tyres, and moreparticularly to compositions comprising a crumb rubber.

Indeed, it is at the current time advantageous for tyre manufacturers tofind solutions to lower the costs of rubber compositions withoutpenalizing the performances of the tyres using these compositions.

It is known in the prior art that crumb rubbers can be used in tyreproduction. For example, document US 2014/0228505 describes the use of acrumb rubber having a size of less than 60 mesh (250 μm) in compositionsfor tyres.

However, simply reducing the size of the crumbs can cause reducedperformances in terms of rheology, in particular during the manufactureof the mixtures.

Presently, the applicants have shown that a composition comprising aparticular crumb rubber makes it possible to obtain compositions whichhave an improved fluidity, enabling facilitated industrial processingand good tear strength.

The invention thus relates to a rubber composition based on at least anelastomer, a reinforcing filler and a crosslinking system and a crumbrubber, said crumb having a particle size distribution such that itcomprises less than 35% by weight of particles having a size of lessthan 50 μm and less than 30% by weight of particles having a size ofgreater than 200 μm.

The invention also relates to a tyre comprising a composition as definedabove, preferably in all or part of the tread thereof.

Preferentially, the tyre according to the invention will be selectedfrom the tyres intended to equip a two-wheeled vehicle, a passengervehicle, or else a “heavy goods” vehicle (that is to say, undergroundtrain, bus, off-road vehicles, heavy road transport vehicles, such aslorries, tractors or trailers), or else aircraft, constructionequipment, heavy agricultural vehicles or handling vehicles.

I—CONSTITUENTS OF THE COMPOSITION

The rubber compositions according to the invention are based on at leastan elastomer, a reinforcing filler and a crosslinking system and a crumbrubber, said crumb having a particle size distribution such that itcomprises less than 35% by weight of particles having a size of lessthan 50 μm and less than 30% by weight of particles having a size ofgreater than 200 μm.

The expression “composition based on” should be understood as meaning acomposition comprising the mixture and/or the product of the in situreaction of the various base constituents used, some of theseconstituents being able to react and/or being intended to react with oneanother, at least partially, during the various phases of manufacture ofthe composition or during the subsequent curing, modifying thecomposition as it is prepared at the start. Thus, the compositions asemployed for the invention may be different in the non-crosslinked stateand in the crosslinked state.

Moreover, for the purposes of the present patent application, the term“phr” means part by weight per hundred parts of elastomers, within themeaning of the preparation of the composition before curing. That is tosay, in the case of the presence of a crumb rubber, that the term “phr”means part by weight per hundred parts of “new” elastomers, thusexcluding from the base 100 the elastomers contained in the crumbrubber.

In the present description, unless expressly indicated otherwise, allthe percentages (%) shown are percentages by weight. Furthermore, anyinterval of values denoted by the expression “between a and b”represents the range of values extending from more than a to less than b(that is to say, limits a and b excluded), whereas any interval ofvalues denoted by the expression “from a to b” means the range of valuesextending from a up to b (that is to say, including the strict limits aand b).

When reference is made to a “predominant” compound, this is understoodto mean, for the purposes of the present invention, that this compoundis predominant among the compounds of the same type in the composition,that is to say that it is the one which represents the greatest amountby weight among the compounds of the same type and in particular morethan 50%, preferably more than 75%. Thus, for example, a predominantpolymer is the polymer representing the greatest weight relative to thetotal weight of the polymers in the composition. In the same way, a“predominant” filler is the one representing the greatest mass among thefillers of the composition. By way of example, in a system comprisingjust one polymer, the latter is predominant for the purposes of thepresent invention and, in a system comprising two polymers, thepredominant polymer represents more than half of the weight of thepolymers. On the contrary, a “minor” compound is a compound which doesnot represent the greatest fraction by weight among the compounds of thesame type.

For the purposes of the present invention, when reference is made to a“predominant” unit (or monomer) within the same compound (or polymer),this is intended to mean that this unit (or monomer) is predominantamong the units (or monomers) forming the compound (or polymer), that isto say it is the one which represents the greatest fraction by weightamong the units (or monomers) forming the compound (or polymer). Thus,for example, a resin predominantly composed of cyclopentadiene units isa resin in which the cyclopentadiene units represent the greatest amountby weight among all the units composing said resin. Similarly, a resinpredominantly composed of units selected from the group consisting ofcyclopentadiene, dicyclopentadiene, methylcyclopentadiene and mixturesthereof is a resin in which the sum of the units selected from the groupconsisting of cyclopentadiene, dicyclopentadiene, methylcyclopentadieneand mixtures thereof represents the greatest number by weight among allthe units composing said resin. In other words, a “predominant” monomeris a monomer which represents the greatest fraction by weight in thepolymer. On the contrary, a “minor” monomer is a monomer which does notrepresent the greatest molar fraction in the polymer.

In the present application, when reference is made to a ratio of theamounts of a compound A and of a compound B, or a ratio between thecontent of a compound A and the content of a compound B, this is alwaysa ratio in the mathematical sense of the amount of compound A over theamount of compound B.

The compounds mentioned in the description can be of fossil or biobasedorigin. In the latter case, they may partially or completely result frombiomass or be obtained from renewable starting materials resulting frombiomass. Polymers, plasticizers, fillers, and the like, are concerned inparticular.

I-1. Elastomer

The elastomer may be selected from the group consisting of dieneelastomers and mixtures thereof.

It is recalled here that elastomer (or “rubber”, the two terms beingregarded as synonymous) of the “diene” type should be understood, in aknown way, as meaning an (one or more is understood) elastomer resultingat least in part (i.e., a homopolymer or a copolymer) from dienemonomers (monomers bearing two conjugated or non-conjugatedcarbon-carbon double bonds).

Diene elastomers can be classified into two categories: “essentiallyunsaturated” or “essentially saturated”. “Essentially unsaturated” isunderstood to mean generally a diene elastomer resulting at least inpart from conjugated diene monomers having a content of units or unitsof diene origin (conjugated dienes) which is greater than 15% (mol %);thus it is that diene elastomers such as butyl rubbers or copolymers ofdienes and of alpha-olefins of EPDM type do not come within thepreceding definition and can in particular be described as “essentiallysaturated” diene elastomers (low or very low content, always less than15%, of units of diene origin). In the category of “essentiallyunsaturated” diene elastomers, a “highly unsaturated” diene elastomer isunderstood in particular to mean a diene elastomer having a content ofunits of diene origin (conjugated dienes) which is greater than 50%.

Given these definitions, diene elastomer capable of being used in thecompositions according to the invention is understood more particularlyto mean:

(a) any homopolymer obtained by polymerization of a conjugated dienemonomer having from 4 to 12 carbon atoms;(b) any copolymer obtained by copolymerization of one or more conjugateddienes with one another or with one or more vinylaromatic compoundshaving from 8 to 20 carbon atoms;(c) a ternary copolymer obtained by copolymerization of ethylene and ofan α-olefin having from 3 to 6 carbon atoms with a non-conjugated dienemonomer having from 6 to 12 carbon atoms, such as, for example, theelastomers obtained from ethylene and propylene with a non-conjugateddiene monomer of the abovementioned type, such as, in particular,1,4-hexadiene, ethylidenenorbornene or dicyclopentadiene;(d) a copolymer of isobutene and of isoprene (butyl rubber) and also thehalogenated versions, in particular chlorinated or brominated versions,of this type of copolymer.

Although it applies to any type of diene elastomer, those skilled in theart of tyres will understand that the present invention is preferablyemployed with essentially unsaturated diene elastomers, in particular ofthe above type (a) or (b).

The following are especially suitable as conjugated dienes:1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-di(C₁-C₅alkyl)-1,3-butadienes, such as, for example, 2,3-dimethyl-1,3-butadiene,2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene,2-methyl-3-isopropyl-1,3-butadiene, aryl-1,3-butadiene, 1,3-pentadieneor 2,4-hexadiene. The following, for example, are suitable asvinylaromatic compounds: styrene, ortho-, meta- or para-methylstyrene,the “vinyltoluene” commercial mixture, para-(tert-butyl)styrene,methoxystyrenes, chlorostyrenes, vinylmesitylene, divinylbenzene orvinylnaphthalene.

The copolymers can contain between 99% and 20% by weight of diene unitsand between 1% and 80% by weight of vinylaromatic units. The elastomersmay have any microstructure, which depends on the polymerizationconditions used, in particular on the presence or absence of a modifyingand/or randomizing agent and on the amounts of modifying and/orrandomizing agent used. The elastomers may be, for example, block,random, sequential or microsequential elastomers and may be prepared indispersion or in solution; they may be coupled and/or star-branched orelse functionalized with a coupling and/or star-branching orfunctionalization agent. “Function” here is preferentially understood tomean a chemical group which interacts with the reinforcing filler of thecomposition.

Preferentially, the elastomer of the composition comprises predominantlyan essentially unsaturated diene elastomer. The elastomer of thecomposition is preferably selected from the group consisting ofpolybutadienes (abbreviated to BRs), synthetic polyisoprenes (IRs),natural rubber (NR), butadiene copolymers, isoprene copolymers andmixtures of these elastomers. Such butadiene and isoprene copolymers aremore preferentially, respectively, butadiene/styrene copolymers (SBRs)and isoprene/styrene copolymers (SIRs).

More preferentially, the predominant elastomer is selected from thegroup consisting of polybutadienes, natural or synthetic syntheticpolyisoprenes and mixtures of these elastomers.

I-2 Reinforcing Filler

The composition according to the invention comprises a reinforcingfiller. Use may be made of any type of reinforcing filler known for itsabilities to reinforce a rubber composition which can be used for themanufacture of tyres, for example an organic filler, such as carbonblack, a reinforcing inorganic filler, such as silica or alumina, oralso a blend of these two types of filler.

Preferably, the content of reinforcing filler is within a rangeextending from 5 to 200 phr, preferably from 20 to 160 phr.

For the needs of the invention, the reinforcing filler is preferentiallyselected from the group consisting of silicas, carbon blacks, andmixtures thereof. More preferentially, the reinforcing filler ispredominantly carbon black, preferably in a content within a rangeextending from 30 to 90 phr. Likewise preferentially, the reinforcingfiller is predominantly silica, preferably in a content within a rangeextending from 30 to 90 phr.

All carbon blacks, in particular “lyre-grade” blacks, are suitable ascarbon blacks. Mention will more particularly be made, among the latter,of the reinforcing carbon blacks of the 100, 200 or 300 series (ASTMgrades), such as, for example, the N115, N134, N234, N326, N330, N339,N347 or N375 blacks, or else, depending on the applications targeted,the blacks of higher series (for example N660, N683 or N772). The carbonblacks might, for example, be already incorporated in an isopreneelastomer in the form of a masterbatch (see, for example, ApplicationsWO 97/36724 or WO 99/16600).

Mention may be made, as examples of organic fillers other than carbonblacks, of functionalized polyvinyl organic fillers, such as describedin Applications WO-A-2006/069792, WO-A-2006/069793, WO-A-2008/003434 andWO-A-2008/003435.

The composition can comprise one type of silica or a blend of severalsilicas. The silica used may be any reinforcing silica known to thoseskilled in the art, especially any precipitated or fumed silica with aBET surface area and a CTAB specific surface area that are both lessthan 450 m²/g, preferably from 30 to 400 m²/g. Mention will be made, ashighly dispersible precipitated silicas (“HDSs”), for example, of theUltrasil 7000 and Ultrasil 7005 silicas from the company Evonik, theZeosil 1165MP, 1135MP and 1115MP silicas from the company Solvay, theHi-Sil EZ150G silica from the company PPG, the Zeopol 8715, 8745 and8755 silicas from the company Huber, treated precipitated silicas, suchas, for example, the silicas “doped” with aluminium described inApplication EP-A-0735088, or the silicas with a high specific surfacearea as described in Application WO 03/16387. The silica preferably hasa BET specific surface of between 45 and 400 m²/g, more preferentiallyof between 60 and 300 m²/g.

These compositions can optionally also comprise, in addition to thecoupling agents, coupling activators, agents for covering the inorganicfillers or more generally processing aids capable, in a known way, byvirtue of an improvement in the dispersion of the filler in the rubbermatrix and of a lowering of the viscosity of the compositions, ofimproving their ability to be processed in the raw state, these agentsbeing, for example, hydrolysable silanes, such as alkylalkoxysilanes,polyols, fatty acids, polyethers, primary, secondary or tertiary amines,or hydroxylated or hydrolysable polyorganosiloxanes.

Those skilled in the art will understand that, as filler equivalent tosilica described in the present section, use might be made of areinforcing filler of another nature, especially organic nature,provided that this reinforcing filler is covered with a layer of silicaor else comprises functional sites, in particular hydroxyl sites, at itssurface which require the use of a coupling agent in order to form thebond between the filler and the elastomer.

The physical state in which the reinforcing filler is provided is notimportant, whether it is in the form of a powder, of microbeads, ofgranules, of beads or any other appropriate densified form.

I-3 Crosslinking System

In the composition of the invention, any type of crosslinking systemknown to those skilled in the art for rubber compositions may be used.

The crosslinking system is preferably a vulcanization system, that is tosay based on sulfur (or on a sulfur-donating agent) and a primaryvulcanization accelerator. Various known secondary vulcanizationaccelerators or vulcanization activators, such as zinc oxide, stearicacid or equivalent compounds, or guanidine derivatives (in particulardiphenylguanidine), may be added to this base vulcanization system,being incorporated during the first non-productive phase and/or duringthe productive phase, as described subsequently.

The sulfur is used at a preferential content of between 0.5 and 10 phr,more preferentially of between 0.5 and 5 phr, in particular between 0.5and 3 phr.

The vulcanization system of the composition according to the inventionmay also comprise one or more additional accelerators, for examplecompounds of the family of the thiurams, zinc dithiocarbamatederivatives, sulfenamides, guanidines or thiophosphates. Use may be madein particular of any compound capable of acting as accelerator of thevulcanization of diene elastomers in the presence of sulfur, especiallyaccelerators of thiazole type and also derivatives thereof, acceleratorsof the thiuram type, and zinc dithiocarbamates. These accelerators aremore preferentially selected from the group consisting of2-mercaptobenzothiazole disulfide (abbreviated to “MBTS”),N-cyclohexyl-2-benzothiazolesulfenamide (abbreviated to “CBS”),N,N-dicyclohexyl-2-benzothiazolesulfenamide (abbreviated to “DCBS”),N-(tert-butyl)-2-benzothiazolesulfenamide (abbreviated to “TBBS”),N-(tert-butyl)-2-benzothiazolesulfenimide (abbreviated to “TBSI”), zincdibenzyldithiocarbamate (abbreviated to “ZBEC”) and mixtures of thesecompounds. Preferably, use is made of a primary accelerator of thesulfenamide type.

I-4 Crumb Rubber

The composition of the invention also comprises a crumb rubber(abbreviated to “crumb” in the remainder of the text).

The crumbs are in the form of granules, optionally made into a sheet ofrubber. Usually, crumb rubbers are derived from milling or micronizationof cured rubber compositions already used for a first application, forexample in tyres; they are a product of the recycling of materials. Thecrumbs thus preferably consist of a composition based on at least oneelastomer and a filler. The crumbs are preferably in the form ofmicroparticles.

The term “microparticles” is intended to mean particles which have asize, namely their diameter in the case of spherical particles or theirlargest dimension in the case of anisometric particles, of a few tens ofor a few hundred microns.

For the needs of the invention, the crumb rubber has a particle sizedistribution such that it comprises less than 35% (preferably less than25%) by weight of particles having a size of less than 50 μm and lessthan 30% (preferably less than 20%) by weight of particles having a sizeof greater than 200 μm.

According to a first preferred embodiment, the composition according tothe invention comprises a crumb rubber which has a particle sizedistribution such that it comprises less than 35% (preferably less than25%) by weight of particles having a size of less than 50 μm and lessthan 30% (preferably less than 20%) by weight of particles having a sizeof greater than 100 μm.

According to a second preferred embodiment, the composition according tothe invention comprises a crumb rubber which has a particle sizedistribution such that it comprises less than 35% (preferably less than25%) by weight of particles having a size of less than 100 μm and lessthan 30% (preferably less than 20%) by weight of particles having a sizeof greater than 200 μm.

In order to obtain the specific crumbs comprising less than 35%(preferably less than 25%) by weight of particles having a size of lessthan 50 μm (where appropriate less than 100 μm) and less than 30%(preferably less than 20%) by weight of particles having a size ofgreater than 200 μm (where appropriate greater than 100 μm), the processstarts with a crumb rubber that is commercially available or is obtainedaccording to the milling or micronization techniques known to thoseskilled in the art, then the fractions of less than 50 μm (whereappropriate less than 100 μm) and greater than 200 μm (where appropriategreater than 100 μm) are removed by screening.

The milling can be carried out by various techniques, in particularcryogenic impact micronization, which make it possible to obtainparticles of small size on rubber materials. Commercial equipment suchas the CUM150 mill from the company Netzsch or the CW250 mill from thecompany Alpine can be used.

The screening can be carried out by various techniques (shaking, suctioncentrifugation); webs or screens having a calibrated mesh size, such asthe commercial products from the company Gericke, can be used for thecentrifugal sieve CSM7/22 MK1, for example the NY 2×1/2 HC 53 μm screen,the 2×1/2 NY 100μ HD screen or the 2×1/2 NY 200μ HD screen.

Preferentially, the crumb is present in a content within a rangeextending from 5% to 40% by weight, preferentially from 10% to 30% andmore preferentially from 15% to 25%. In a standard composition intendedfor tyres, these weight contents correspond to contents of from 5 to 100phr. Below 5 phr, the saving made would not be significant enough,whereas above 100 phr, it is possible for the cohesion properties of thecomposition to be penalized. Thus, the crumb content is preferablywithin a range extending from 10 to 90 phr, preferentially from 15 to 90phr, more preferentially from 20 to 80 phr and very preferentially from30 to 70 phr for optimum operation of the invention.

As discussed above, the crumbs preferably consist of a composition basedon an elastomer and a filler. They may also comprise all the ingredientsnormally used in rubber compositions, such as plasticizers,antioxidants, vulcanization additives, etc.

Thus, the crumb comprises an elastomer, preferentially a dieneelastomer. This elastomer preferentially represents at least 30% byweight, more preferentially at least 35% by weight, even morepreferentially at least 45% by weight of the weight of the crumb, saidpercentage been determined according to Standard ASTM E1131. It ispreferentially selected from the group consisting of polybutadienes,polyisoprenes including natural rubber, butadiene copolymers andisoprene copolymers. More preferentially, the molar content of units ofdiene origin (conjugated dienes) present in the diene elastomer isgreater than 50%, preferably between 50% and 70%.

According to one preferential embodiment of the invention, the crumbcontains between 5% and 80% by weight of filler, more preferentiallybetween 10% and 75%, and very preferentially between 15% and 70%.

The term “filler” is intended to mean herein any type of filler, whetherreinforcing (typically having nanometric particles, with aweight-average size preferably of less than 500 nm, in particularbetween 20 and 200 nm) or nonreinforcing or inert (typically havingmicrometric particles, with a weight-average size preferably of greaterthan 1 μm, for example between 2 and 200 μm). The weight-average size ofthe nanometric particles is measured in a manner well known to thoseskilled in the art (by way of example, according to patent applicationWO 2009/083160 paragraph 1.1). The weight-average size of themicrometric particles can be determined by mechanical screening.

Mention will in particular be made, as examples of fillers known asreinforcing to those skilled in the art, of carbon black or of areinforcing inorganic filler, such as silica or alumina in the presenceof a coupling agent, or mixtures thereof.

According to one preferential embodiment of the invention, the crumbcomprises, by way of filler, a reinforcing filler, in particular acarbon black or a mixture of carbon blacks.

The carbon black or the mixture of carbon blacks preferentiallyrepresents more than 50%, more preferentially more than 80%, even morepreferentially more than 90% by weight of the weight of the reinforcingfiller of the crumb. According to a more preferential embodiment of theinvention, the reinforcing filler consists of a carbon black or amixture of carbon blacks.

Very preferentially, the carbon black is present in the crumb in acontent ranging from 20% to 40% by weight, more preferentially from 25%to 35% by weight.

All carbon blacks, in particular blacks of the HAF, ISAF, SAF, FF, FEF,GPF and SRF type, conventionally used in rubber compositions for tyres(“tyre-grade” blacks) are suitable as carbon blacks.

The crumb may contain all the other usual additives which are part of arubber composition, in particular for tyres. Among these usualadditives, mention may be made of liquid or solid plasticizers,non-reinforcing fillers such as chalk, kaolin, protective agents,vulcanization agents. These additives may also be in the crumb in theform of a residue or of a derivative, since they were able to reactduring the steps of producing the composition or of crosslinking thecomposition from which the crumb is derived.

With regard to the constituents of the crumb, it is preferable, for theneeds of the invention, for the crumb to have an acetone extract ofbetween 3% and 30% by weight, more preferentially within a rangeextending from 5% to 25% by weight.

Likewise, it is preferable for the crumb to have a chloroform extract ofbetween 5% and 85% by weight, more preferentially within a rangeextending from 5% to 50% by weight.

The crumbs may be simple ground/micronized rubber materials, without anyother treatment. It is also known that these crumbs can undergo atreatment in order to modify them. This treatment can consist of achemical functionalization or devulcanization modification. It may alsobe a thermomechanical, thermochemical, biological, etc., treatment.

According to a preferred first embodiment of the invention, it ispossible to use a crumb which has not undergone any modification bythermal and/or mechanical and/or biological and/or chemical treatment.

According to this first embodiment, it is preferable for the crumb tohave an acetone extract of between 3% and 15% by weight, morepreferentially within a range extending from 3% to 10% by weight.Likewise, it is preferable for the crumb to have a chloroform extract ofbetween 3% and 20% by weight, more preferentially within a rangeextending from 5% to 15% by weight. Preferentially, the chloroformextract of the crumb rubber has a weight-average molecular weight (Mw)of less than 10 000 g/mol, preferably less than 8000 g/mol.

According to the first embodiment, it is preferable for the ratio of thechloroform extract to the acetone extract, expressed as weightpercentage, to be less than 1.5.

According to a second embodiment of the invention, it is possible to usea crumb which has a morphology modified by thermal and/or mechanicaland/or biological and/or chemical treatment.

According to this second embodiment, it is preferable for the crumb tohave an acetone extract of between 5% and 20% by weight, morepreferentially within a range extending from 10% to 18% by weight.Likewise, it is preferable for the crumb to have a chloroform extract ofbetween 15% and 85% by weight, more preferentially within a rangeextending from 15% to 50% by weight. Preferentially, the chloroformextract of the crumb rubber has a weight-average molecular weight (Mw)of greater than 10 000 g/mol, preferably greater than 20 000 g/mol andmore preferentially greater than 30 000 g/mol.

According to the second embodiment, it is preferable for the ratio ofthe chloroform extract to the acetone extract, expressed as weightpercentage, to be greater than or equal to 1.5, preferably greater than2.

Likewise preferably according to this second embodiment, the crumb has aMooney viscosity (conventionally expressed in Mooney units, MU) ofbetween 40 and 90, preferably between 45 and 75 and more preferentiallybetween 50 and 70.

I-5 Other Possible Additives

The rubber compositions in accordance with the invention optionally alsocomprise all or a portion of the normal additives customarily used inelastomer compositions intended especially for the manufacture oftreads, such as, for example, pigments, protective agents, such asanti-ozone waxes, chemical antiozonants or antioxidants, plasticizingagents other than those described above, anti-fatigue agents,reinforcing resins, or methylene acceptors (for example novolac phenolicresin) or donors (for example HMT or H3M).

The composition according to the invention may also comprise aplasticizing system. This plasticizing system may be composed of ahydrocarbon-based resin with a Tg of greater than 20° C., in addition tothe specific hydrocarbon-based resin described above, and/or aplasticizing oil.

Of course, the compositions in accordance with the invention can be usedalone or as a blend (i.e., as a mixture) with any other rubbercomposition which can be used for the manufacture of tyres.

It is obvious that the invention relates to the rubber compositionsdescribed above both in the “raw” or non-crosslinked state (i.e., beforecuring) and in the “cured” or crosslinked, or also vulcanized, state(i.e., after crosslinking or vulcanization).

II—PREPARATION OF THE RUBBER COMPOSITIONS

The compositions are manufactured in appropriate mixers, using twosuccessive phases of preparation which are well known to those skilledin the art: a first phase of thermomechanical working or kneading(sometimes referred to as “non-productive” phase) at high temperature,up to a maximum temperature of between 110° C. and 200° C., preferablybetween 130° C. and 180° C., followed by a second phase of mechanicalworking (sometimes referred to as “productive” phase) at lowertemperature, typically below 110° C., for example between 60° C. and100° C., during which finishing phase the crosslinking or vulcanizationsystem is incorporated; such phases have been described, for example, inApplications EP-A-0 501 227, EP-A-0 735 088, EP-A-0 810 258, WO00/05300or WO00/05301.

The first (non-productive) phase is preferably carried out in severalthermomechanical steps. During a first step, the elastomers, thereinforcing fillers and the crumb (and optionally the coupling agentsand/or other ingredients, with the exception of the crosslinking system)are introduced into an appropriate mixer, such as a customary internalmixer, at a temperature between 20° C. and 100° C. and preferablybetween 25° C. and 100° C. After a few minutes, preferentially from 0.5to 2 min, and a rise in the temperature to 90° C. or to 100° C., theother ingredients (that is to say, those which remain, if not all wereput in at the start) are added all at once or in portions, with theexception of the crosslinking system, during a mixing ranging from 20seconds to a few minutes. The total duration of the kneading, in thisnon-productive phase, is preferably between 2 and 10 minutes at atemperature of less than or equal to 180° C. and preferentially of lessthan or equal to 170° C.

After cooling the mixture thus obtained, the crosslinking system is thenincorporated at low temperature (typically less than 100° C.), generallyin an external mixer, such as an open mill; the combined mixture is thenmixed (productive phase) for a few minutes, for example between 5 and 15min.

The final composition thus obtained is subsequently calendered, forexample in the form of a sheet or slab, in particular for laboratorycharacterization, or else extruded, in order to form, for example, arubber profiled element used in the manufacture of semi-finishedproducts for tyres. These products may then be used for the manufactureof tyres, according to techniques known to those skilled in the art,with the advantage of the invention, namely good tack of the layers onone another before curing of the tyre.

The crosslinking (or curing) is carried out in a known way at atemperature generally of between 130° C. and 200° C., under pressure,for a sufficient time which can vary, for example, between 5 and 90 min,as a function in particular of the curing temperature, of thecrosslinking system adopted, of the kinetics of crosslinking of thecomposition under consideration or else of the size of the tyre.

The examples which follow illustrate the invention without, however,limiting it.

III—EXEMPLARY EMBODIMENTS OF THE INVENTION II-1 Characterization of theCrumb Rubbers and the Rubber Compositions of Examples

In the examples, the crumb rubbers are characterized as indicated below.

Measurement of the Particle Size:

The particle size weight distribution can be measured using a laserparticle size analyzer of the mastersizer 3000 type from the companyMalvern. The measurement is carried out by the liquid route, diluted inalcohol after an ultrasound pretreatment for 1 min in order to guaranteeparticle dispersion. The measurement is carried out in accordance withStandard ISO-13320-1.

Measurement of the Acetone Extract:

The acetone extract content is measured according to Standard ISO1407 bymeans of an extractor of soxhlet type.

A sample test specimen (between 500 mg and 5 g) is introduced into anextraction chamber and then placed in the extractor tube of the soxhlet.A volume of acetone equal to two or three times the volume of theextractor tube is placed in the collector of the soxhlet. The soxhlet issubsequently assembled and then heated for 16 h.

The sample is weighed after extraction. The acetone extract contentcorresponds to the loss of weight of the sample during the extraction,related back to the initial weight.

Measurement of the Chloroform Extract:

The chloroform extract content is measured according to Standard ISO1407by means of an extractor of soxhlet type.

A sample test specimen (between 500 mg and 5 g) is introduced into anextraction chamber and then placed in the extractor tube of the soxhlet.A volume of chloroform equal to two or three times the volume of theextractor tube is placed in the collector of the soxhlet. The soxhlet issubsequently assembled and then heated for 16 h.

The sample is weighed after extraction. The chloroform extract contentcorresponds to the loss of weight of the sample during the extraction,related back to the initial weight.

Measurement of the Average Molecular Weights of the Chloroform Extract:

The molecular weights are determined by size exclusion chromatography,according to a Moore calibration and according to Standard ISO16014.

The weight-average molecular weight (Mw) of the chloroform extract iscarried out by size exclusion chromatography (SEC) with a refractiveindex (RI) detector. The system is composed of an Alliance 2695 systemfrom Waters, a column oven from Waters and also of an RI 410 detectorfrom Waters. The set of columns used is composed of two PL GEL MIXED Dcolumns (300×7.5 mm 5 μm) followed by two PL GEL MIXED E columns(300×7.5 mm 3 μm) from the company Agilent. These columns are placed ina column oven thermostated at 35° C. The mobile phase used isnon-anti-oxidized tetrahydrofuran. The flow rate of the mobile phase is1 ml/min. The RI detector is also thermostated at 35° C.

The chloroform extract is dried under a nitrogen stream. The dry extractis then taken up at 1 g/I in non-anti-oxidized tetrahydrofuran at 250ppm for 2 hours with stirring. The solution obtained is filtered using asyringe and a single-use 0.45 μm PTFE syringe filter. 100 μl of thefiltered solution are injected into the conditioned chromatographicsystem at 1 ml/min and 35° C.

The Mw results are provided by integration of the chromatographic peaksdetected by the RI detector above a value of 2000 g/mol. The Mw iscalculated from a calibration carried out using polystyrene standards.

Measurement of the Carbon Black Weight Fraction:

The carbon black weight fraction is measured by thermogravimetricanalysis (TGA) according to Standard NF T-46-07, on an instrument fromthe company Mettler Toledo, model “TGA/DSC1”. Approximately 20 g ofsample are introduced into the thermal analyzer, then subjected to athermal program from 25 to 600° C. under an inert atmosphere(pyrolyzable phase), then from 400 to 750° C. and an oxidizsingatmosphere (oxidizable phase). The weight of the sample is continuouslymeasured throughout the thermal programme. The black content correspondsto the loss of weight measured during the oxidizable phase related backto the initial weight of sample.

In the examples, the rubber compositions are characterized, beforeand/or after curing, as indicated below.

Measurement of the Melt Flow Index:

This measurement is suitable for the measurement of melt flow indexcommonly used in the plastics industry for the characterization of theextrudability, in particular of thermoplastics. The measurement isdescribed in Standard ASTM D1238 (or NF T 51-016) and modified asfollows.

The sample of the elastomeric mixture is heated, in a capillaryrheometer, to a regulated temperature (approximately 90 deg. C.). Themass which has flowed (extrudate) through a cylindrical die (diameter 2mm) made of tungsten carbide is subsequently measured using a loadedpiston. The melt flow index value corresponds to the displacement of thepiston under the effect of the load, in hundredths of a millimetre, fora time of 10 seconds (corresponds to a flow rate). The index 100 isgiven for the melt flow index of the control composition; an index ofgreater than 100 indicates a greater melt flow index and a lower indexindicates a poorer melt flow index.

Measurement of Elongation at Break (Tensile Tests):

These tensile tests make it possible to determine the elasticitystresses and the properties at break. Unless otherwise indicated, theyare carried out in accordance with French Standard NF T 46-002 ofSeptember 1988. Processing the tensile recordings also makes it possibleto plot the curve of modulus as a function of the elongation. Themodulus used here is the nominal (or apparent) secant modulus measuredin first elongation, calculated by reducing to the initial cross sectionof the test specimen. The nominal secant moduli (or apparent stresses,in MPa) are measured in first elongation at 50% and 100% elongation,respectively denoted MSA50 and MSA100.

The breaking stresses (in MPa) and the elongations at break (in %) aremeasured at 23° C.±2° C. according to Standard NF T 46-002 or at 100° C.

III-2 Preparation of the Crumbs

As indicated above, the specific crumbs of the invention are prepared bycryogenic milling then successive screenings so as to keep only thedesired sizes between 50 and 200 microns, and preferentially between 50and 100 microns or between 100 and 200 microns. Any composition of thecrumb may be suitable for the preparation of these crumbs. For theimplementation examples, the crumbs used are of a heavy-weight vehicletyre tread composition as presented in Table 1 below:

TABLE 1 Crumb composition NR (1) 80 BR (2) 20 Carbon black (3) 48Antioxidant (4) 3 Stearic acid (5) 2 Zinc oxide (6) 3 Accelerator (7) 1Sulfur 1.5(1) NR: Natural rubber(2) BR: polybutadiene, CB24 from the company Lanxess; 96% of 1,4-cis-;Tg=−107° C.(3) Carbon black, ASTM N234 grade(4) N-(1,3-Dimethylbutyl)-N′-phenyl-p-phenylenediamine (Santoflex 6-PPD)from the company Flexsys(5) Stearin, Pristerene 4931 from the company Uniqema(6) Zinc oxide, industrial grade—the company Umicore(7) N-Cyclohexyl-2-benzothiazolesulfenamide (Santocure CBS from thecompany Flexsys)

This composition was milled. The milling is carried out on a piece ofequipment, CUM150, from the company Netzsch using spike diameters of 3mm and a mill rotation speed of 15 000 rpm. The matter flow rate isabout 50 kg/h and the equipment is cooled in order to guarantee a milloutlet gas temperature of −60° C. The milled material was then screenedas described above, in order to obtain the crumbs 1 to 5 presented inTable 2 below:

In Table 2 below, a size distribution indicated as 0 to 200 μm(respectively 0 to 100 μm or 0 to 50 μm) means that this crumb has aparticle size distribution such that it comprises less than 35%(preferentially less than 25%) by weight of particles having a size ofgreater than 200 μm (or respectively greater than 100 μm or greater than50 μm).

Likewise, a size distribution indicated as 50 to 100 μm means that thiscrumb has a particle size distribution such that it comprises less than35% (preferably less than 25%) by weight of particles having a size ofless than 50 μm and less than 30% (preferably less than 20%) by weightof particles having a size of greater than 100 μm.

Likewise, a size distribution indicated as 100 to 200 μm means that thiscrumb has a particle size distribution such that it comprises less than35% (preferably less than 25%) by weight of particles having a size ofless than 100 μm and less than 30% (preferably less than 20%) by weightof particles having a size of greater than 200 μm.

TABLE 2 Crumbs Crumb 1 Crumb 2 Crumb 3 Crumb 4 Crumb 5 Size distribution0 to 200 μm 0 to 100 μm 0 to 50 μm 50 to 100 μm 100 to 200 μm Acetoneextract 4.6% 4.6% 4.6% 4.6% 4.6% Chloroform extract 6.3% 6.3% 6.3% 6.3%6.3% Mw of the chloroform 7000 g/mol 7000 g/mol 7000 g/mol 7000 g/mol7000 g/mol extract Carbon black weight  30%  30%  30%  30%  30% fraction

III-3 Rubber Compositions

The compositions are manufactured with introduction of all of theconstituents onto an internal mixer, with the exception of thevulcanization system. The vulcanizing agents (sulfur and accelerator)are introduced into an external mixer at low temperature (theconstituent rolls of the mixer being at around 30° C.).

The object of the examples presented in Table 3 is to compare thedifferent rubber properties of control compositions (T1 to T4) to theproperties of compositions in accordance with the invention (C1 and C2).The properties measured, before and after curing, are presented in Table4.

TABLE 3 T1 T2 T3 T4 C1 C2 NR (1) 80 80 80 80 80 80 BR (2) 20 20 20 20 2020 Carbon black (3) 48 48 48 48 48 48 Crumb 1 0 53 0 0 0 0 Crumb 2 0 053 0 0 0 Crumb 3 0 0 0 53 0 0 Crumb 4 0 0 0 0 53 0 Crumb 5 0 0 0 0 0 53Antioxidant (4) 3 3 3 3 3 3 Stearic acid (5) 2.6 2.6 2.6 2.6 2.6 2.6Zinc oxide (6) 3.3 3.3 3.3 3.3 3.3 3.3 Accelerator (7) 1.15 1.15 1.151.15 1.15 1.15 Sulfur 1.9 1.9 1.9 1.9 1.9 1.9 (1) NR: Natural rubber (2)BR: polybutadiene, CB24 from Lanxess; 96% of 1,4-cis-; Tg = −107° C. (3)Carbon black, ASTM N234 grade (4)N-(1,3-Dimethylbutyl)-N′-phenyl-p-phenylenediamine (Santoflex 6-PPD)from the company Flexsys (5) Stearin, Pristerene 4931 from the companyUniqema (6) Zinc oxide, industrial grade - Umicore (7)N-Cyclohexyl-2-benzothiazolesulfenamide (Santocure CBS from Flexsys)

TABLE 4 T1 T2 T3 T4 C1 C2 Melt flow index (base 100 104 85 91 134 128100) Elongation at break 100 103 106 107 104 106 23° C. (base 100)Elongation at break 100 111 123 86 121 118 100° C. (base 100)

Compared with the control compositions, it is noted that onlycompositions C1 and C2 in accordance with the invention make it possibleto improve the melt flow index while at the same time preserving verygood elongations at break at 23° C. and 100° C.

1.-29. (canceled)
 30. A rubber composition based on at least anelastomer, a reinforcing filler, a crosslinking system and a crumbrubber, wherein the crumb rubber has a particle size distribution suchthat it comprises less than 35% by weight of particles having a size ofless than 50 μm and less than 30% by weight of particles having a sizeof greater than 200 μm.
 31. The rubber composition according to claim30, wherein the crumb rubber has a particle size distribution such thatit comprises less than 25% by weight of particles having a size of lessthan 50 μm and less than 20% by weight of particles having a size ofgreater than 200 μm.
 32. The rubber composition according to claim 30,wherein the crumb rubber is present in a content ranging from 5% to 40%by weight.
 33. The rubber composition according to claim 30, wherein thecrumb rubber is present in a content ranging from 5 to 100 phr.
 34. Therubber composition according to claim 30, wherein the crumb rubber hasan acetone extract of between 3% and 30% by weight.
 35. The rubbercomposition according to claim 30, wherein the crumb rubber has achloroform extract of between 5% and 85% by weight.
 36. The rubbercomposition according to claim 30, wherein the crumb rubber has notundergone any modification by a treatment selected from the groupconsisting of thermal, mechanical, biological, and chemical treatmentsand combinations thereof.
 37. The rubber composition according to claim36, wherein the crumb rubber has an acetone extract of between 3% and15% by weight.
 38. The rubber composition according to claim 36, whereinthe crumb rubber has a chloroform extract of between 3% and 20% byweight.
 39. The rubber composition according to claim 36, wherein thecrumb rubber has a ratio of a chloroform extract to an acetone extract,expressed as weight percentage, of less than 1.5.
 40. The rubbercomposition according to claim 36, wherein the crumb rubber has achloroform extract of which the weight-average molecular weight is lessthan 10,000 g/mol.
 41. The rubber composition according to claim 30,wherein the crumb rubber has a morphology modified by a treatmentselected from the group consisting of thermal, mechanical, biological,and chemical treatments and combinations thereof.
 42. The rubbercomposition according to claim 41, wherein the crumb rubber has anacetone extract of between 5% and 20% by weight.
 43. The rubbercomposition according to claim 41, wherein the crumb rubber has achloroform extract of between 15% and 85% by weight.
 44. The rubbercomposition according to claim 41, wherein the crumb rubber has a ratioof a chloroform extract to an acetone extract, expressed as weightpercentage, of greater than or equal to 1.5.
 45. The rubber compositionaccording to claim 41, wherein the crumb rubber has a chloroform extractof which the weight-average molecular weight is greater than 10,000g/mol.
 46. The rubber composition according to claim 41, wherein thecrumb rubber has a Mooney viscosity of between 40 and
 90. 47. The rubbercomposition according to claim 30, wherein the crumb rubber has a carbonblack weight fraction ranging from 20% to 40% by weight.
 48. The rubbercomposition according to claim 30, wherein the crumb rubber has aparticle size distribution such that it comprises less than 35% byweight of particles having a size of less than 50 μm and less than 30%by weight of particles having a size of greater than 100 μm.
 49. Therubber composition according to claim 30, wherein the crumb rubber has aparticle size distribution such that it comprises less than 35% byweight of particles having a size of less than 100 μm and less than 30%by weight of particles having a size of greater than 200 μm.
 50. Therubber composition according to claim 30, wherein the elastomerpredominantly comprises an elastomer selected from the group consistingof essentially unsaturated diene elastomers.
 51. The rubber compositionaccording to claim 50, wherein the predominant elastomer is selectedfrom the group consisting of polybutadienes, polyisoprenes, butadienecopolymers, isoprene copolymers and mixtures thereof.
 52. The rubbercomposition according to claim 51, wherein the predominant elastomer isselected from the group consisting of polybutadienes, polyisoprenes andmixtures thereof.
 53. The rubber composition according to claim 30,wherein the reinforcing filler is selected from the group consisting ofsilicas, carbon blacks, and mixtures thereof.
 54. The rubber compositionaccording to claim 30, wherein a content of reinforcing filler is withina range extending from 5 to 200 phr.
 55. The rubber compositionaccording to claim 30, wherein a predominant reinforcing filler iscarbon black at a content within a range extending from 30 to 90 phr.56. The rubber composition according to claim 30, wherein a predominantreinforcing filler is silica at a content within a range extending from30 to 90 phr.
 57. A tire comprising the rubber composition according toclaim
 30. 58. The tire according to claim 57, wherein the rubbercomposition constitutes all or part of a tread of the tire.